The present invention generally relates to an electrophotography type image forming apparatus, and more particularly to an image forming apparatus capable of easily preventing the quality of a picture from deteriorating.
In an image forming apparatus, such as a laser beam printer and an electrophotography copying machine, using an electrophotography processes, a charging unit, a developing unit and a transfer charging unit are successively arranged along a surface of a photosensitive body in a moving direction thereof. The image forming apparatus also has an optical system which casts the optical image of a document onto the surface of the photosensitive body between the charging unit and the developing unit. A station where the optical image casting is performed by the optical system is termed an exposing station. Then, the charging unit uniformly applies a charge to the surface of the photosensitive body, and the optical system casts the optical image onto the charged surface of the photosensitive body so that a electrostatic latent image corresponding to the optical image is formed. The electrostatic latent image formed on the surface of the photosensitive body is developed by the developing unit. That is, the toner from the developing unit is deposited on the electrostatic latent image so that a toner image ( developed image ) corresponding to the electrostatic latent image is formed. Then, a sheet to which a charge is applied to a back thereof by the transfer charger comes into contact with the toner image formed on the surface of the photosensitive body. As a result, the toner image leaves the surface of the photosensitive body and is transferred to the surface of the sheet. After the toner image is transferred to the sheet, the sheet is separated from the photosensitive body and the toner image is pressed into the sheet by a fusing unit. By the process as has been described above, an image is formed onto the sheet.
The optical system is housed in a housing to protect it against dust and prevent light leakage, or a shield plate is provided between the optical system and a part on the photosensitive body where the optical image is cast. A projection opening is provided on the housing or the shield plate so that the optical system can cast the optical image through the projection opening onto the photosensitive body.
A suspended toner is leaked through a gap formed between an edge of an opening on a housing of the developer unit and the photosensitive body. Since the exposing station is adjacent to a developing station where the developing is performed by the developer unit, there is a possibility of the suspended toner going through the projection opening in the housing of the optical system. To improve the reliability of conveying sheets and to facilitate a paper jam operation, an image forming apparatus such as a laser beam printer having a special structure is proposed. In this image forming apparatus having the special structure, the exposing station above mentioned is provided under the photosensitive body and a transfer station where the toner image is transferred from the photosensitive body to the sheet is provided above the photosensitive body. Particularly, in the image forming apparatus having the special structure described above, a gap between the edge of the opening on the housing of the developer unit and the photosensitive body is above the projection opening of the housing of the optical system so that the toner leaked through the gap directly falls on the projection opening and the suspended toner subsides and easily goes into the housing of the optical system. Accordingly, the projection opening formed on the housing of the optical system is sealed up by a cylindrical lens, which is one of the optical elements of the optical system, or a glass plate. In addition, a dustproof glass is detachably provided at a predetermined position so as to cover the projection opening. When the toner from the developer unit adheres to the surface of the dustproof glass, the dustproof glass is removed and the toner is wiped from the dustproof glass. Then, the dustproof glass from which the toner is wiped is set at the predetermined position again.
The suspended toner also adheres to the charger unit so that the charging characteristic of the charger unit deteriorates.
Conventionally, the dustproof glass and the charger unit are, respectively, removed from the housing of the image forming apparatus and wiped, and then they are reset as before. The dustproof glass and the charger can also be exchanged. However, because of the positions where they are set, it is difficult to either remove or exchange them. Accordingly, a cleaning mechanism for cleaning the dustproof glass has been proposed in Japanese Laid- Open Patent Application No. 57-146282. In this cleaning mechanism, when a process unit is removed and then set as before, a cleaning member, which is formed of polyurethane foam or the like, provided on the process unit wipes the surface of the dustproof glass. However, it is difficult for the cleaning mechanism to completely wipe the toner adhered on the surface of the dustproof glass away from the surface thereof. Instead, there are many cases where the toner is spread on the dustproof glass. In the image forming apparatus such as a laser beam printer in which a high resolution is required, due to the dust on the optical system, picture quality considerably deteriorates.
In a small size laser printer or the like, the user exchanges components thereof so that the developing unit is exchanged when there is no toner in the developing unit.